I see a few others jumped in with some good summaries while I was putting my response together. Here's what I was preparing for you:
tkj, perhaps these pages might help answer some of your questions. If these links jog other questions in your mind, let us know.
from Joe's people section:
http://www.beatlesbible.com/pe.....len-klein/
from Joe's history section:
http://www.beatlesbible.com/19.....et-london/
http://www.beatlesbible.com/19.....ow-london/
http://www.beatlesbible.com/19.....s-manager/
There are few more history pages with Apple in the title if you want to look them up.
Hope this ...